Ball grid array resistor network

Abstract

A ball grid array resistor network has a planar substrate formed of an organic material. The substrate preferably is a printed circuit board. The substrate has a top and bottom surface. A ball pad is located on the bottom surface. A low temperature resistor is located on the bottom surface and is connected to the ball pad. A solder mask is located over the first surface except for the ball pads. A conductive ball is attached to the ball pad. A reflowed solder paste connects the conductive ball to the ball pad. Several embodiments of the invention are shown.

1 . A resistor network comprising: 
 a) a planar substrate formed of an organic material having a first and second surface;    b) a thin film resistor attached to and located on the first surface, the resistor having a first end and a second end and a center section, the resistor having a resistivity between 25 ohms per square and 100,000 ohms per square;    c) a first ball pad covering the first end of the resistor and a second ball pad covering the second end of the resistor such that the center section is located between the first and second ball pads;    d) a solder mask located over the first surface, the solder mask having apertures located over the ball pads, the solder mask further covering the center section of the resistor;    e) a conductive ball located adjacent to each of the ball pads; and    f) a reflowed solder paste partially surrounding each of the conductive balls and the ball pads, the reflowed solder paste connecting the conductive ball to the ball pad.    
   
   
       2 . The resistor network of  claim 1 , wherein a laser cut extends into the resistor, the laser cut adjusting the resistance of the resistor.  
   
   
       3 . The resistor network of  claim 1 , wherein the conductive ball is formed from a high temperature melting point solder.  
   
   
       4 . The resistor network of  claim 1 , wherein the resistor is electroplated.  
   
   
       5 . The resistor network of  claim 1 , wherein the solder paste has a low temperature melting point.  
   
   
       6 . The resistor network of  claim 1 , wherein the substrate is a printed circuit board.  
   
   
       7 . The resistor network of  claim 1 , wherein a heat dissipating metal layer is attached to the second surface.  
   
   
       8 . The resistor network of  claim 1 , wherein the substrate is formed from a thermally conductive material.  
   
   
       9 . A resistor network comprising: 
 a) a planar substrate formed of an organic material having a top and bottom surface;    b) a ball pad located on the bottom surface;    c) a low temperature resistor located on the bottom surface, the low temperature resistor having an end that extends under the ball pad, the resistor having a resistivity between 25 ohms per square and 100,000 ohms per square;    d) a solder mask located over the bottom surface except for the ball pad; and    e) a solder bump attached to the ball pad, the solder bump formed from a reflowed solder paste.    
   
   
       10 . The resistor network of  claim 9 , wherein the substrate is a printed circuit board.  
   
   
       11 . The resistor network of  claim 9 , wherein the ball pad is formed from a copper foil and the resistor is a thin film deposited onto the copper foil.  
   
   
       12 . The resistor network of  claim 9 , wherein the ball pad and resistor are formed by subtractive etching using photolithography.  
   
   
       13 . The resistor network of  claim 9 , wherein the resistor is laser trimmed.  
   
   
       14 . The resistor network of  claim 9 , wherein a heat dissipating metal layer is attached to the top surface.  
   
   
       15 . The resistor network of  claim 9 , wherein the substrate is formed from a thermally conductive material.  
   
   
       16 . A resistor network comprising: 
 a) a planar substrate formed of an organic material having a first and second surface;    b) a laser reflective layer laminated to the first surface;    c) a resistor mounted on the laser reflective layer, the resistor having a first end, a second end and a center section;    d) a first ball pad covering the first end of the resistor and a second ball pad covering the second end of the resistor;    e) a solder mask located over the laser reflective layer and the first surface, the solder mask having apertures located over the ball pads, the solder mask further covering the center section of the resistor;    f) a conductive ball located adjacent to each of the ball pads; and    g) a reflowed solder paste partially surrounding each of the conductive balls and the ball pads, the reflowed solder paste connecting the conductive ball to the ball pad.